Establish long term steady state cultures of mouse bone marrow and infect with Friend Leukemia virus, Ableson virus, and other MuLV. Monitor cultures for evidence of transformation and characterize the target cells. Manipulate the culture system to select for transformed cells. Establish continuous cultures from other hematopoietic tissues and infect with MuLV. Develop agarose colony assay for in vitro transformation with Abelson virus. Characterize Abelson virus transformed cells for differentiation markers and virus expression. Identify the target cell for A-MuLV transformation. Develop continuous cultures of murine B or T lymphocytes and infect with A-MuLV or Thymotropic MuLV derived from AKR mice. Develop in vitro transformation system of hemopoietic microenvironmental cells with Soule myeolid leukemia virus.